Tanning process



Patented Dec. 5, 1933 UNITED STATES PATENT OFFICE 1,935,390 TANNING PROCESS poration of Delaware No Drawing.

8 Claims.

This invention relates to the tanning of hides, skins, and the like using a new class of tanning materials.

According to the invention, leather is produced by the tanning of hides and skins in the presence of artificial tanning agents which have been subjected to the action of bleaching agents in order to remove their color. The invention is not limited to any particular class of artificial tan- 10 ning agents as it has been found that the use of at least some classes of bleaching agents will improve the color of practically all the artificial tanning agents at present in use.

Artificial tanning agents, the so-called synl5 tans, are products resulting from the sulfonation of aromatic hydrocarbons, with or without condensation with aldehydes, cellulose, phthalic anhydride substances and the like. Representative tanning agents of this class are the Neradols which are condensation products of phenol-and cresolsulfonic acids with aldehydes, and similar products in which the aromatic hydrocarbon or phenol has been condensed with cellulose. In my prior applications Serial No. 512,500 filed J anuary 30, 1931 Serial No. 512,752 filed January 31, 1931 and Serial No. 512,753 filed January 31, 1931 and in the prior application of Jaeger and Witzel Serial No. 518,291 filed February 25, 1931, tanning processes have been described in which residues from the purification of aromatic hydrocarbons such as crude anthracene, crude phenanthrene, crude naphthalene and the like have been condensed with cellulose or other carbohydrates, in some cases with further condensation with aldehydes such as formaldehyde, acct; aldehyde, furfural and the like. The present invention is particularly applicable to artificial tanning materials of this class since the impurities in the raw materials used may tend to darken the color of the tanning solution although the active tanningmaterials themselves usually possess a sufiiciently light color. It is an advantage of thetanning processes of the present. invention that they not only produce a lighter tannage when artificial tanning agents from pure raw materials are used but also produce leather of sufficiently light color from impure materials containing considerable amounts of non-tannins.

In carrying out the invention the hides, suitably delimed and hated, are suspended in vats containing the bleached tanning materials, either with or without the addition of vegetable tans, and the tannage is conducted as in ordinary processes using commercial synthetic and natural 55 materials. The preparation 01 the bleached tan- Application February 28, 1931 Serial No. 519,266

ning materials of the present invention is described in my co-pending application Serial No. 518,292 filed February 25,1931, and consequently is not repeated here, but it is to be noted that these materials when used in conjunction with vegetable tans produce a much clearer solution and cause a pronounced lightening in color of the entire vat. It has not been definitely ascertained whether this action is due to a partial bleaching of the vegetable material itself or whether the lightening in color is due only to a solvent action of the bleached artificial tanning material on the natural tannins, and the invention is not limited to any definite theory of action. It has been noted, however, that if too large an excess of oxidizing agent is used the tanning power or the solution is lessened, and consequently it is to be presumed that a certain amount of bleaching action is exerted on the solution as a whole.

The bleaching agents that may be used in preparing bleached tanning materials for use according to the present invention may be those ordinarily employed in bleaching processes. In

, addition to the hypohalites, which are ordinarily used for this purpose, other oxidizing agents may 0 be used such as chlorine in acid solution, chromic acid, potassium permanganate, etc. and i1 desired mixtures may be used. In the case of chromic acid, the reduction product is itself a tanning material.

The constitution of the bleached artificial tanning materials used in the present invention is not definitely known as the unbleached condensation products themselves are not subject to structural analysis. I am of the opinion, however, that the bleaching action first attacks certain colored impurities in the condensation products, this view being supported :by the fact that .no diminution in tanning power is noted when only small amounts of bleaching agent are used whereas the most pronounced lightening in color 'is efiected with the addition of the first amounts of bleaching agent.

The invention will be described in greater detail in,con'nection with the following specific examples.

Example 1 50 parts of the black granular mass prepared by reacting 50 parts of cellulose in the form of 103 old sulfite paper with 750 parts of concentrated sulfuric acid while the mass is being subjected to agitation and cooling. This material after completion of the reaction is further admixed with 134 parts or the residue from the fur-tural e purification of anthracene and containing phenanthrene, carba'zole, dead oils, etc. The mass is stirred continuously until all of the residue is dissolved. It is then poured into 10,000 parts of water, the excess acid is neu'iralized with lime and the neutral product is filtered. The calcium salt thus obtained is transformed into the sodium salt by means of sodium carbonate. The latter salt upon evaporation produces a brownish mass which is the sodium salt of the condensation product of the sulphonated cellulose and the aromatic hydrocarbon. The salt obtained amounts to 175 parts by weight of the cellulose and anthracene residue. Preparation of this material is described in Example 1 of the J aeger application Serial No. 512,500 filed January 30, 1931 and which is the condensation product of the residue from the purification of crude anthracene by means of furfural, cellulose and sulfuric acid are mixed with 500 parts by weight of water and vigorously stirred for one hour. 400 parts of a water solution containing 10.84 parts of NaOCl is vigourously stirred in. The stirring is continued for about two hours, the color of the liquor changing from dark brown or black to dark yellow or very light brown. On evaporation, a solid is obtained which is readily soluble in water and shows good tanning power.

Instead of using sodium hypochlorite, chlorine may be passed in, the solution being kept sufficiently alkaline to assure good absorption of the chlorine. The amount of chlorine passed in should, of course, correspond to about 10% sodium hypochlorite.

Instead of using hypohalites, potassium permanganate or chromic acid may be used.

Hides, suitably delimed and bated, are suspended in aqueous solutions of bleached artificial tanning agents prepared according to the above process, with or without the addition of such natural tanning agents as oak bark extract, chestnut, hemlock, gambier, quebracho, sumac. etc. The tannage is effected in a liquor having a pH value of approximately 2-5 according to the ordinary counter-current process; that is to say, the fresh hides are suspended in the most nearly spent tanned liquors and are advanced from day to day towards the most freshly prepared and concentrated vats. A leather is produced which is light in color, of good appearance and of excellent strength.

Example 2 Tannage is effected from a vat or a series of vats containing a condensation product of cellulose and the residue from the vaporization of crude naphthalene and sulfuric acid, prepared according to Example 1 of the application of A. O. Jaeger, Serial No. 512,752 in the form of its sodium salt which has been bleached as described in the foregoing example. The procedure for the preparation of the unbleached material is as follows:

50 parts of cellulose in the form of old sulfi'e paper are introduced into 750 parts of concentrated sulfuric acid through agitation. This addition should also be accompanied by constant cooling. At the conclusion of the addition, 134 parts of the residue from the sublimation of crude naphthalene for the manufacture of phthalic anhydride bytthe well known catalytic oxidation are added with stirring and the stirring is continued until the whole of the residue is dissolved. The mass is then poured into 10,000 parts of water and the excess acid is neutralized with lime. After neutralization, the material is filtered and the calcium salt of the condensation product of the cellulosic material and the naphthalene residue thus obtained is transformed into the sodium salt by means of sodium carbonate. Upon evaporation of the filtered solution a light brown mass is obtained, which is the desired sodium salt of the condensation product. The yield obtained amounts to 160 to 170% by weight of the cellulose and naphthalene residues. The condensation product is an excellent tanning agent for leather and may be used alone or in admixture with other tanning agents. A good leather is produced even when no vegetable tanning extract is used, but for the best leathers the addition of suitable amounts of vegetable tanning extracts is recommended.

Example 3 A condensation product of cellulose treated with phthalic anhydride, the residue from the solvent purification of anthracene and sulfuric acid, prepared as described in Example 1 of the application of A. O. Jeager Serial No. 512,753 filed January 31, 1931, in the form of its sodium salt is treated wijh a hypochlorite as described in Example 1.

The preparation of the condensation product of cellulose with phthalic anhydride and sulfuric acid may be described as follows:-750 parts of 107.3% sulfuric acid are cooled to 20 C. and 34.3 parts of pure phthalic anhydride or the equivalent quantity of impure phthalic anhydride are added. The mixture is further cooled to 16 C., and 50 parts of cellulose in the form of old sulfite paper, or cotton linters, are added during a period of 4 hours. The mixture thus obtained is stirred during a further period of 8 hours, at the end of which time it will have been transferred into a blackish liquid smelling somewhat of S02. The liquid is treated with 134 parts of the residue from the purification of crude anthracene the addition being made slowly during a period of 5 hours and the temperature being kept at all times below 20 C. The material should also be stirred until the reaction is complete. The resulting mass is a deep black viscous liquid. The liquid should be poured with constant stirring into 2,000 parts of water maintained as cold as possible, and milk of lime prepared from 360 parts of CaO is added. Neutralization of the acid mixture is completed by the addition of CaCO3. The neutralized product is filtered, and the liquid may be evaporated to produce a solid product. If desired, the calcium in the reaction product may be exchanged for sodium by the treatment of the liquid prior to evaporation with sodium carbonate.

Tannage is effected from a series of vats containing the above described condensation product and also containing an astringent tan such as quebracho, hemlock, larch, etc. The color of the so'. tion of the vegetable tanning material is considerably improved by the addition of the bleached artificial tanning agent, and its rate of peneration is materially improved by reason of the more rapid tanning properties of the artificial material, which effect a partial tannage in advance of the vegetable agent and thus increases the perviousness of the inner portions of the hides to the latter material.

Example 4 The condensation product of cellulose, the residue from the solvent purification of crude anthracene, sulfuric acid and formaldehyde, as described in Example 1 of the Jaeger and Witzel application Serial No. 518,291 filed February 25, 1931, above referred to, in the form of its sodium or calcium salt is treated with a hypochlorite as described in Example 1. The brownish black liqnor is transformed into a light brown or brownish yellow. and retains its tanning powers.

The preparation of the condensation product of cellulose with the residue from the solvent purification of crude anthracene and formaldehyde is as follows:-'Approximately 50 parts of cellulose in the form of old sulfite paper are introduced into 750 parts of concentrated sulfuric acid with constant agitation and cooling. Thereupon 134 parts of the residue from the furfural purification of anthracene and containing phenanthrene, carbazole, dead oils, etc. are stirred in, and the stirring continued until the residue dissolves. The mass is then poured into 10,000 parts of water and the excess acid is neutralized with lime and filtered. The calcium salt so obtained is transformed into the sodium salt by means of sodium carbonate. Upon evaporation of the filtered solution a brownish mass is obtained which is a sodium salt of the condensation product. The yield amounts to 175% by weight of the cellulose and anthracene residue. 50 parts of the intermediate condensation product are then treated with 250 parts of 40% sulfuric acid and 10 parts of 30% formaldehyde solution, the treatment being accompanied by vigorous agitation. The material is heated to C. for about one-half of an hour and the stirring is continued as the material gradually cools down. The odor of the aldehyde should disappear in about two hours. A black mass is obtained which'is readily soluble in water and which is an excellent tanning agent. This mass is stirred into 700 parts of cold water, and milk of lime containing 200 parts of calcium oxide is added. Completion of the neutralization of the acid condensation product is effected by the addition of calcium carbonate. After filtering, the liquid may be evaporated to produce a solid product, and preferably the calcium is exchanged for sodium by treatment with soda ash, followed by a second filtration. The sodium salt is readily soluble in water and is an excellent taming agent. The tanning agent may be used alone or in admixture with other tanning agen's. The formaldehyde may be substituted by acetaldehyde or a mixture of acetaldehyde and formaldehyde may be used.

Tannage is effected using the above material, as described in previous examples, with or without the addi'ion of vegetable tanning agents.

What is claimed as new is:

1. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate and at least one aromatic hydrocarbon with sulfuric acid, which condensation product has been subjected to the action of a bleaching agent.

2. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a bleached condensation product of at least one carbohydrate, a phthalic anhydride substance, and at least one aromatic hydrocarbon with sulfuric acid.

3. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a bleached condensation product of at least one carbohydrate and at least one aromatic hydrocarbon with sulfuric acid and an aldehyde.

4. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate, at least one substance belonging to the group consisting of residues from solvent purification of crude anthracene with phenanthrene and carbazole solvents, residues from solvent purification of crude anthracene with phenanthrene solvents,residues from the vaporization of impure anthracene, residues from the vaporiza tion of crude naphthalene, with sulfuric acid, which condensation product has been subjected to the action of a bleaching agent.

5. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate, a phthalic anhydride substance, and at least one substance belonging to the group consisting of residues from solvent purification of crude anthracene with phenanthrene and carbazole solvents, residues from solvent purification of crude anthracene with phenanthrene solvents, residues from the vaporization of impure anthracene, residues from the vaporization of crude naphthalene, with sulfuric acid, which condensation product has been subjected to the action of a bleaching agent.

6. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate and at least one aromatic hydrocarbon with sulfuric acid, which condensation product has been subjected to the action of a hypohalite.

7. A process of tanning hides, which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate, at least one substance belonging to the group consisting of residues from solvent purification of crude anthracenewith phenanthrene and carbazole solvents, residues from solvent purification of crude anthracene with phenanthrene solvents, residues from the vaporization of impure anthracene, residues from the vaporization of crude naphthalene, with sulfuric acid, which condensation product has been subjected to the action of a hypohalite.

8. A process of tanning hides. which comprises treating the hides with an aqueous solution containing a condensation product of at least one carbohydrate, a. phthalic anhydride substance, and at least one substance belonging to the group consisting of residues from solvent purification of crude anthracene with phenanthrene and carbazole solvents, residues from solvent purification of crude anthracene with phenanthrene solvents, residues from the vaporization of impure anthracene, residues from the vaporization of crude naphthalene, with sulfuric acid, which condensation'product has been subjected to the action of a hypohalite.

ALPHONS O. JAEGER. 

